BIOCHEMISTRY
Sanger, F., and Tuppy, H. (1951a), Biochem. J. 49, 463. Sanger, F., and Tuppy, H. (1951b), Biochem. J . 49, 481. Spackman, D. H., Stein, W. H., and Moore, S. (1958), Anal. Chem. 30,1190. Stewart, G . A. (1960), British Med. Bull. 16,196. Tometsko, A., and Delihas, N. (1967), Anal. Biochem. 18,12.
Wang, Y.,Hsu, J., Chang, W., Cheng, L., Li, H., Hsing, C., Shi, P., Loh, T., Chi, A., Li, C., Yieh, Y., and Tang, K. (1965), Sci. Sinica (Peking) 14, 1887. Zahn, H., Bremer, H., and Zabel, R. (1965a), Z . Naturforsch. 20b, 653. Zahn, H . , Brinkhoff, O., Meienhofer, J., Pfeiffer, E. F., Ditschuneit, H., and Gloxhuber, C. (1965b), Z . Naturforsch. 20b, 666.
P-Aspartyl Peptide Formation from an Amino Acid Sequence in Ribonuclease* Edward E. Haley and Betty J. Corcoran
ABSTRACT : Exhaustive
enzymic hydrolysates of bovine ribonuclease have a much higher P-aspartyl peptide content than digests of other proteins of known structure previously studied. P-Aspartyl di-, tri-, and tetrapeptides are shown to derive from 22 to 34 of a certain
z
P
revious experiments (Haley et al., 1966; Pisano et al., 1966), in which P-aspartyl peptides were found in enzymic digests of several proteins, failed to demonstrate conclusively that these linkages originated from the natural amino acid sequence of the molecules. In proteins of known sequence molar yields of Asp(Gly),l the most abundant peptide, were always below 4 % of the theoretical, a value too low to exclude with certainty the occasional presence of a side-chain glycine attached in cico by transamidation (Loewy et al., 1966). Our results indicated but did not prove that /?-aspartyl bonds formed during the digestions and did not preexist. Because the nonenzymic conversion of Asn-Gly to Asp(G1y) was found to proceed at approximately ten times the rate of the conversion of Asp-Gly to the @ isomer it was felt that bovine ribonuclease, which has one -Am-Gly- and no -Asp-Gly- sequences (Hirs et al., 1960; Smyth et a[., 1962, 1963), might yield more Asp(G1y) than hemoglobin or lysozyme, which have -Asp-Gly- but no -Am-Gly- sequences (Konigsberg
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* From the Veterans Administration Hospital, West Haven, Connecticut, and the Department of Biochemistry, Yale University, New Haven, Connecticut. Received June 6, 1967. This work was supported in part by a research grant (AM-1277) from the National Institutes of Health. * Abbreviations used : Asp-Gly, a-L-aspartylglycine; Asp(Gly), 8-L-aspartylglycine; Asp(Gly-Gln), 8-L-aspartylglycyl-L-glutamine, etc.; VI
